1. Field of the Invention:
The present invention relates to an automatic disc playback system for drawing a desired disc on a tray from a rack, which houses a multiplicity of discs placed on respective trays, into a disc feed unit, taking the disc from the tray, returning the tray into its storage position in the rack, moving the disc feed unit with the disc held thereon to a disc playback unit, and then loading the disc from the disc feed unit into the disc playback unit for reproducing audio, video, and/or character information recorded on the disc.
2. Description of the Prior Art:
There have recently been developed various automatic disc playback systems for selecting a desired disc from a multiplicity of loaded discs and automatically playing back the selected disc with a disc playback unit.
FIG. 18 of the accompanying drawings shows one such conventional automatic disc playback system loaded with a multiplicity of selectable discs. The automatic disc playback system, generally designated by the reference numeral 200, has a single rack 201 housing a number of discs 203 placed on respective trays 202. The trays 202 have respective circular recesses 202a for receiving the respective discs 203 therein, the recesses 202a having respective outer circular steps for engaging the respective outer circumferential edges of the discs 203 to hold the discs 203 in position on the trays 202. The automatic disc playback system 200 also includes a vertically movable disc feed unit 205 that is positioned on one side of the rack 201.
In operation, the disc feed unit 205 is brought into a position in front of a desired disc 203 placed on its tray 202, and the desired disc 203 is drawn, together with the tray 202, out of the rack 200 onto the disc feed unit 205. The disc feed unit 205, which supports the disc 203 on the tray 202, is then lowered to a position adjacent to a disc playback unit 206 disposed beneath the rack 201. The disc 203 is then inserted, along with the tray 202, from the disc feed unit 205 into the disc playback unit 206. In the disc playback unit 206, the disc 203 on the tray 202 is placed on a turntable 207, and rotated by the turntable 207 and played back to reproduce the recorded information.
The disc 203 that is desired to be played back is always accompanied by the corresponding tray 202 when it is withdrawn from the rack 201, carried by the disc feed unit 205, inserted into the disc playback unit 206, and played back thereby. To allow the disc 203 placed on the tray 202 to be reliably returned into its storage position in the rack 201, the trays 202 should be spaced at relatively large intervals or distances in the rack 201. However, increasing the intervals or distances between the trays 202 in the rack 201 results in a reduction in the disc storage capacity of the rack 201. Stated otherwise, it is necessary to increase the height of the rack 201 in order to increase the disc storage capacity of the rack 201. It would be possible to minimize the distances between the trays 202 by highly accurately controlling the position of disc feed unit 205 as it moves. However, a highly complex control mechanism would be required and it would be difficult to move the disc feed unit 205 at high speeds. Another problem is that when the tray 202 and the disc 203 placed thereon are fed by the disc feed unit 205, the tray 202 and the disc 203 may be vibrated, and hence may possibly be displaced in position and/or damaged.
The rack 201 has tray locking means (not shown) for locking the trays 202 in the rack 201. Since the tray locking means are associated with the trays 202, respectively, it is also necessary to keep the distances between the trays 202 wide enough to accommodate the tray locking means, thus limiting the disc storage capacity of the rack 201. The tray locking means that are combined with the respective trays 202 are constructed of a large number of parts, which make the automatic disc playback system 200 highly costly.
Each of the trays 202 can hold only one disc 203 in position thereon because the disc 203 is positioned only by the circular step around the recess 202a which engages the outer circumferential edge of the disc 203. The automatic disc playback system 200 is limited in its use as the rack 201 cannot store different types of discs having different outside diameters.
Two discs of different outside diameters may be placed on a tray which has two concentric circular recesses having respective outer circular steps for engaging the respective outer circumferential edges of the discs. Inasmuch as the two concentric circular recesses have respective bottom surfaces lying at different levels, the tray is relatively thick. Therefore, a rack loaded with a number of such trays has a limited disc storage capacity.
The applicant has proposed an automatic disc playback system with a plurality of juxtaposed racks for increased disc storage capacity, as disclosed in Japanese patent application No. 2-262387.